Burden resistor temperature compensation algorithm

An automatic temperature compensation method for automatically adjusting a trip threshold of a circuit breaker, comprising:

• storing in a memory a trip threshold representing a current level that, if exceeded when a maximum temperature is present, causes the circuit breaker to trip;
• reading a temperature from a temperature sensor circuit to produce a temperature sensor reading indicative of at least the temperature of a circuit board on which the temperature sensor circuit is disposed, the circuit board including a burden resistor circuit disposed proximate the temperature sensor circuit such that there is temperature coupling between a burden resistor of the burden resistor circuit and a temperature sensor of the temperature sensor circuit;
• converting, as a function of the temperature sensor reading and a determined relationship between resistance of the burden resistor circuit and temperature, the temperature sensor reading into a corresponding burden resistor value indicative of a resistance of the burden resistor circuit disposed on the circuit board and electrically coupled to a secondary output of a current transformer of the circuit breaker;
• adjusting the trip threshold as a function of the burden resistor value to produce a temperature-compensated trip threshold;
• storing the temperature-compensated trip threshold in the memory;
• causing the circuit breaker to trip when a primary current sensed by the current transformer exceeds the temperature-compensated trip threshold;
• and
• determining a temperature inflection point representing an intersection between a temperature sensor curve and a burden resistance curve, the temperature sensor curve plotting a voltage output of the temperature sensor circuit against temperature and the burden resistance curve plotting resistance across the burden resistor circuit against temperature;
• and
• matching the temperature sensor reading to the burden resistor value about the temperature inflection point.

A method of automatically adjusting a trip current threshold of a circuit breaker, comprising:

• receiving, in a microcontroller, a temperature signal from a temperature sensor circuit, the temperature signal being indicative of a temperature sensed by the temperature sensor circuit, a temperature sensor of the temperature sensor circuit being disposed proximate a burden resistor circuit such that there is temperature coupling between a burden resistor of the burden resistor circuit and the temperature sensor;
• calculating, by the microcontroller, as a function of the temperature signal and a determined relationship between resistance of the burden resistor circuit and temperature, a burden resistance value indicative of a resistance of the burden resistor circuit;
• responsive to the determining, adjusting at least one trip current threshold of the circuit breaker as a function of the burden resistance value to produce an adjusted trip current threshold;
• storing the adjusted trip current threshold in memory;
• and
• wherein the burden resistance value corresponds to a percentage of burden resistance relative to a nominal burden resistance, and wherein the adjusting the at least one trip current threshold includes decreasing the at least one trip current threshold until the burden resistance value matches an estimated burden resistance value that is initialized to a high temperature burden resistance value at a maximum temperature.

An automatic temperature compensation method for automatically adjusting a trip threshold of a circuit breaker, comprising:

• storing in a memory a trip threshold representing a current level that, if exceeded when a maximum temperature is present, causes the circuit breaker to trip;
• reading a temperature from a temperature sensor circuit to produce a temperature sensor reading indicative of at least the temperature of a circuit board on which the temperature sensor circuit is disposed, the circuit board including a burden resistor circuit disposed proximate the temperature sensor circuit such that there is temperature coupling between a burden resistor of the burden resistor circuit and a temperature sensor of the temperature sensor circuit;
• converting, as a function of the temperature sensor reading and a determined relationship between resistance of the burden resistor circuit and temperature, the temperature sensor reading into a corresponding burden resistor value indicative of a resistance of the burden resistor circuit disposed on the circuit board and electrically coupled to a secondary output of a current transformer of the circuit breaker;
• adjusting the trip threshold as a function of the burden resistor value to produce a temperature-compensated trip threshold;
• storing the temperature-compensated trip threshold in the memory;
• causing the circuit breaker to trip when a primary current sensed by the current transformer exceeds the temperature-compensated trip threshold;
• and
• wherein the burden resistor value is a percentage burden resistance representing a percentage off set from a burden resistance at an ambient temperature.

An automatic temperature compensation method for automatically adjusting a trip threshold of a circuit breaker, comprising:

• storing in a memory a trip threshold representing a current level that, if exceeded when a maximum temperature is present, causes the circuit breaker to trip;
• reading a temperature from a temperature sensor circuit to produce a temperature sensor reading indicative of at least the temperature of a circuit board on which the temperature sensor circuit is disposed, the circuit board including a burden resistor circuit disposed proximate the temperature sensor circuit such that there is temperature coupling between a burden resistor of the burden resistor circuit and a temperature sensor of the temperature sensor circuit;
• converting, as a function of the temperature sensor reading and a determined relationship between resistance of the burden resistor circuit and temperature, the temperature sensor reading into a corresponding burden resistor value indicative of a resistance of the burden resistor circuit disposed on the circuit board and electrically coupled to a secondary output of a current transformer of the circuit breaker;
• adjusting the trip threshold as a function of the burden resistor value to produce a temperature-compensated trip threshold;
• storing the temperature-compensated trip threshold in the memory;
• causing the circuit breaker to trip when a primary current sensed by the current transformer exceeds the temperature-compensated trip threshold;
• and
• wherein the burden resistor circuit includes a field-effect transistor having a resistance across its source and drain terminals when the field-effect transistor is turned on.